In the Northern hemisphere, viral epidemics cause up to 80% of all respiratory illnesses. The most common infections are caused by six viral groups: rhinovirus (RVs), respiratory syncytial virus, influenza virus, parainfluenza virus, corona virus, and adenovirus.
Influenza is a contagious respiratory illness caused by a group of viruses that are part of the virus family orthomyxoviridae. Influenza viruses are significant human respiratory pathogens that cause both seasonal, endemic infections and periodic, unpredictable pandemics. The worst pandemic on record, in 1918, killed approximately 50 million people worldwide. Human infections caused by H5N1 highly pathogenic avian influenza viruses have raised concerns about the emergence of another pandemic. Influenza viruses cause epidemic respiratory illness every winter in most countries on the planet. Influenza often begins with cold-like symptoms and progresses to involve the lungs. Most patients develop a chronic cough that can last for weeks. Pneumonia can develop and is a common cause of death among more susceptible people. It can cause mild to severe illness, and at times can lead to death. Certain groups, such as the very young, the very old and the immunocompromised, are at higher risk for contracting the virus and developing serious complications from infection.
Previous attempts to treat influenza infection focused on neuraminidase inhibitors to prevent the release of new infectious virus and halt viral replication. Other attempts focused on adamantane M2 ion channel blockers, such as amantadine and rimantadine. However, problems arose with viral resistance to treatment. Influenza viruses constantly mutate. In addition, antigenic changes take place each year in the annual dominant influenza strain. As a result, vaccines generated to stimulate immune responses to viral antigens must be prepared yearly. Annual influenza shots are recommended for all persons at risk, but the vaccines are based on last year's virus strains with no guarantee that they will protect against newly emergent viruses. During the winter flu season, people who develop respiratory illness require therapeutic treatment to reduce their ability to spread the disease. Thus, a need exists for new therapeutic drugs that limit the effects of influenza virus infection by targeting aspects of the host immune response.